(a) Field of the Invention
The present invention relates to an offset compensation method of a current sensor and a motor driving system incorporating the same, and more particularly, to an offset compensation method of a current sensor capable of determining whether the offset compensation of the current sensor is abnormal.
(b) Description of the Related Art
Generally, a motor is used for driving an electric vehicle, a hybrid vehicle, and the like. An inverter converts a DC current into a 3-phase AC current (u phase, v phase, and w phase) and supplies the 3-phase current to the motor through a power cable, where a motor controller controls the inverter using pulse width modulation (PWM). Further, the 3-phase current is sensed by a current sensor.
The current sensor has its own offset or has an offset due to aging of the current sensor and other hardware over time. Therefore, when current does not flow by the offset compensation of the current sensor, the current measured by the current sensor needs to be 0. A control of the motor may be stabilized, fuel consumption may be reduced, and accidents may be prevented by the offset compensation of the current sensor.
The offset compensation of the current sensor is performed every time the ignition is turned on (IG on), and an average value of an output of the current sensor for a predetermined time after the IG on is obtained, where the offset is compensated using the average value. However, when there is a disturbance in the offset compensation while the average value of the output of the current sensor is obtained, the offset compensation typically is smaller or larger than a normal value. Herein, factors causing the abnormality of the offset compensation may include noise, such as external noise or internal noise, a connector fastening defect due to vibration, heat, aging, corrosion, and the like, a change of an offset value, due to aging of the current sensor, and other factors.
FIGS. 5-9 are diagrams useful for illustrating deficiencies of the related art. In particular, FIG. 5 illustrates the output of a current sensor when the offset compensation abnormality of the current sensor occurs due to external noise. FIG. 6 illustrates the output of the current sensor when there is a connector fastening defect, and FIG. 7 illustrates a 3-phase current when the motor is controlled abnormally. It may be appreciated that when the offset compensation abnormality occurs as described above, the output of the current sensor illustrated in FIGS. 5 and 6, and the 3-phase current illustrated in FIG. 7 are different from the respective outputs of the current sensor illustrated in FIG. 8 and the 3-phase current illustrated in FIG. 9, where FIGS. 8-9 reflect outputs in which an offset compensation abnormality does not occur.
As described above, when the offset compensation abnormality of the current sensor occurs, the motor current control is abnormal, and therefore current consumption is increased and a state of charge (SOC) of a high voltage battery is reduced, such that fuel consumption is reduced. Further, when the control of the motor current is performed abnormally, the motor may be impacted by noise, vibration, and harshness (NVH), such that drivability may be deteriorated. Further, a protective logic of the inverter may malfunction due to a difference between a measured current and a control current, and in severe cases, the inverter may be damaged due to overcurrent and overtemperature, such that a vehicle may be shut down.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.